JERUSALEM — Palestinian President Mahmoud Abbas agreed to resume peace talks with Israel only after U.S. Secretary of State John Kerry gave him a letter guaranteeing that the basis of the negotiations will be Israel’s pre-1967 borders, two senior Palestinian officials said Saturday.

The officials, both of whom are close to the Palestinian leader and privy to internal discussions, said the U.S. letter also stipulated that both sides are to refrain from taking any steps that would jeopardize the outcome of the talks. Israel is not to issue new tenders for Jewish settlements in the West Bank, while the Palestinians are not to pursue diplomatic action against Israel at any international organizations, the officials said on condition of anonymity because they are not authorized to brief the media.

“The talks with Kerry were about to collapse, and the letter came as a lifeline in the last-minute bargaining,” one of the Palestinian officials said.

There was no immediate comment from the State Department, but U.S. officials have said in the past that Kerry would reiterate standing American positions on the goals for renewed talks, including that a Palestinian state should be negotiated on the basis of Israel’s borders before the 1967 Mideast war, when Israel captured the Gaza Strip, West Bank and east Jerusalem.

After a round of intense shuttle diplomacy, Kerry announced Friday that Israel and the Palestinians had agreed on a basis for returning to the peace process, which broke down five years ago. The two sides are to meet — likely in the coming week — to work out final details on actually resuming their negotiations on the toughest issues of the Israeli-Palestinian conflict.

Kerry would not give details on the agreement on the negotiations’ framework. “The best way to give these negotiations a chance is to keep them private.” he said. “We know that the challenges require some very tough choices in the days ahead. Today, however, I am hopeful.”

The Palestinians long refused to return to the negotiating table unless Israel agreed to several preconditions, including that the talks be based on Israel’s pre-1967 borders. Israel frequently called for talks to resume without preconditions, insisting that all core issues should be resolved through dialogue.

Speculation has been rife for weeks that the sides would find a way to sidestep Israel’s reluctance to offer assurances of the 1967 lines as the framework for talks by having the guarantee provided by the United States.

Israeli Prime Minister Benjamin Netanyahu faces sharp opposition from within his majority coalition to such a move. One key ally, Economics Minister Naftali Bennett, has threatened to pull his Jewish Home Party out of the government altogether if the prime minister agrees to the border conditions.

The basis of the negotiations themselves — not the core issues at the heart of the conflict — has been a major impediment to resuming talks. On Thursday evening, the Palestinian leadership balked at dropping a main condition: They demanded a guarantee that negotiations on borders between a Palestinian state and Israel would be based on the cease-fire line that held from 1949 until the 1967 war.

Kerry’s announcement late Friday suggested that the question had been resolved, although the top U.S. diplomat offered no details.

Netanyahu issued a statement Saturday evening welcoming Kerry’s announcement and thanking him for his efforts, saying he “views the resumption of the political process at this time a vital strategic interest.”

Earlier Saturday, Israel’s intelligence and strategic affairs minister offered a few details on the framework. He confirmed that Israel would release some Palestinian prisoners, but said it will not meet other long-standing Palestinian demands before negotiations resume, such as a settlement freeze or defining the 1967 borders as the basis for talks.

Yuval Steinitz told Israel Radio that prisoners Israel has agreed to release include some who “have been sitting in jail for dozens of years,” He did not say how many would be freed.

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